Clothes washing machines are generally known in the art to operate by letting into the washing tub a first amount of water together with the clothes to be washed and the required washing products, and then handling and processing the clothes until they are thoroughly clean. At the end of the washing program, the liquor used in the process is let off outside by means of a pump via an appropriate outlet pipe.
Equally well known in the art is the fact that all parameters of the washing process, i.e. the washing time, the number of rinses, the temperature, and the mechanical action, the chemical action of the washing products and aids are closely correlated with each other and markedly affected by what may be considered as being the determining factor the amount of clothes to be washed.
As a matter of fact, while it is fully apparent that the amount of clothes to be washed also determines the amount of water to be used, it has to be duly considered that the amount of water used in the process determines the amount of energy that is required to heat up that amount of water to a pre-established temperature. Further, the amount of washing product added can be validly brought into a mutual relation with the amount of water and a number of other factors. Finally, it should be noted that even the washing time (the duration of the washing process) is directly affected by the amount of water used and, accordingly, the washload (the amount of clothes) because it is generally known that the presence of just a modest washload inside a rotating drum of a clothes washing machine implies that such a washload is submitted to a mechanical action that is by far stronger than the one acting—with a less marked effect, of course—on a washload that fills up the entire drum.
It can therefore be stated that a reasonably exact knowledge of the amount of clothes loaded into the drum of the washing machine to be washed is practically a pre-condition to be known to set a washing program that causes the washing machine to operate in such a manner as to ensure optimum washing results under minimization of the machine operating requirements in terms of water, washing product and energy usage, as well as time needed to complete the washing process.
As a result, a sound determination of this factor becomes a basic step towards the ability for any other aspect of the washing process to be further improved.
A number of patent publications are known, which use different approaches to tackle the problem of determining the amount and type of the washload, mainly using a measurement of the amount of water totally absorbed by said washload.
Known from GB 2 076 648 (Miele & Cie.) is a front-loading clothes washing machine with a drum rotating about a horizontal axis and provided with such arrangements and operating provisions that, by measuring in a preliminary phase the amount of water that is on the whole absorbed by the washload, enable it to trace back—through proper processing and on the basis of previously measured experimental data—to an information correlating with the kind of washload in the drum.
Such method, however, has the following major drawbacks that put serious limitations to the practical effectiveness thereof:
1. A first drawback is that the measurement of the amount of water absorbed by the washload has, in all cases, to be carried out by causing the drum to become partially submerged in the underlying water bath contained in the washing tub; this condition is obviously required in order to let the clothes loaded in the drum interact with said water and cause the water itself to be absorbed by the washload held in the drum. However, this determines a water usage that is by far greater than the one actually needed, since use is made here of not only an amount of water such as needed to fully soak the washload, but also the amount of water that is needed to fill the bottom portion of the washing tub up to a level enabling the surface of the water in the tub to reach up to an adequate height above the bottom edge of the drum.
2. A second such drawback lies in the method being used; the amount of washload is not actually measured, but rather just processed out through a correlation with the amount of water absorbed by a plurality of washloads that differ from each other as far as both the amount of clothes involved and the kind and properties of the clothes in said washloads are concerned, as determined experimentally in a set of exhaustive test runs carried out beforehand. It can be readily appreciated that such correlation is a source of approximations, and related inaccuracies, not only as far as the methods used for the experiments, the calculations, and extrapolations carried out are concerned, but also due to the fact that, in any case, the calculated value does not take into account the great variability in the aptitude of the various types of fabrics in the washloads to absorb water. As a result, what is actually calculated is in all cases a conventional and not an actually measured value.
3. A third such drawback, owing to water having to be successively filled in the tub a number of times in order to restore the proper level such that each refill step is separated from the subsequent one by respective periods of rotation of the drum, is the proposed method turns out to be quite time consuming.
Known from the disclosure in GB 2 051 413 (Licentia) is a clothes washing machine that is substantially similar to the above described, and is practically adapted to control the amount of detergent to be dispensed into the wash tub based on the amount of water that is let into the same tub. Even in this case, it is not the amount of clothes introduced in the drum for washing that is measured. Rather, such information is worked out by a data processing method that is fully equivalent to the one described above, having the same drawbacks.
Known from the disclosure in EP 1 350 881 A1 is a method for measuring the washload in a front-loading clothes washing machine adapted to: determine the amount of water absorbed by the washload by subtracting, from the total amount of water let into the washing tub, the so-called free amount of water, i.e. the amount that is present in the tub, measured by a pressure switch or level probe; estimate the specific water absorption of the washload; calculate an equivalent (conventional) washload, i.e. load of clothes; and based on the result of this calculation, select and carry out a corresponding washing program.
Furthermore, all of the above processing steps are carried out on the basis of an estimation of the expected final values, which is obtained by detecting and evaluating the dynamic behavior obtained by calculating their derivatives versus time.
However, even this method has a number of practical limitations, such as the following: the equation relating the absorbed amount of water with the amount of water detected by the pressure switch or probe (free water) is admittedly (cf. the above-cited patent at page 2, lines 30 et seq.) involving a number of approximations owing to the interaction between absorbed water and free water; and further, a second approximation derives from an interpolation, using experimental data, based on the specific absorption, i.e. the ratio:                absorbed water/weight of washload        
However, such parameter does not represent any constant data for each actual washload, but is rather a value that varies in accordance with the total amount of water filled in the washing tub (cf. above mentioned patent, page 3, lines 9 et seq., and in particular lines 14 and 15).
It may therefore be readily appreciated that, in the actual practice, the approximations introduced in this way, along with the generally acknowledged method-related limitations, altogether bring about an inaccuracy of such an extent as to impair a real effectiveness of the invention disclosed therein.
Briefly, the invention disclosed in the above-cited patent provides for somehow measuring a so-called “equivalent load” (cf. claim 1), but not the actual washload introduced in the machine.
In addition, even in this case the method suffers a drawback in that, owing to the need for the clothes to be soaked from the water bath in the washing tub, the tub has to be filled up to a level which is adequately higher than the lower limit or edge of the drum inside the tub, and this most obviously implies a fully appreciable water usage involving in turn a respective, but useless energy usage, which would preferably be avoided if water were filled into the tub only in such amount as strictly required to just soak the washload, and no more.
Finally, there is still a further drawback, and which is shared by all of the afore considered concepts. In fact, when the washing tub is filled, even partially, with water to such a level as to rise above the lower edge of the drum, the rotation of the same drum brings about an instability condition and a difference in the level being actually perceived, resulting in a instability in the pressure on the pressure or level control switch and an error in the signal delivered by the latter.
From US 2001/0052249A1 a washing machine is known which is able to avoid the undesirable condition found during a spray pretreatment portion of the wash cycle called “suds lock”. When this condition occurs, contact of the fluid with the spinning basket acts to further increase the amount of suds which thus raises the height of the sudsy fluid toward the basket. The eventual result of this unstable process is that suds build up beyond the bottom of the basket and climb between the sides of the basket and tub. This large amount of suds acting between the spinning basket and the fixed tub produces a significant drag force on the basket. This drug force is large enough to cause the clutch to slip and, thus causing the basket to slow down considerably. This slipping of the clutch due to excessive suds between the spinning basket and the tub is called “suds lock”.
Moreover, the machine is able to determine the size of the load, regardless of the type of fabric materials contained in the load. However, the disclosure only applies to, washing machines provided with a basket rotating only on vertical axis; and not on an horizontal axis, which is customary in Europe.